This invention relates generally to a method for improving thin film or coating adhesion on substrates, and more particularly to such a method for improving adhesion of thin films, such as diamond, TiN or yttria stabilized zirconia films, on substrates for use as cutting tool coatings, wear resistant coatings, corrosion resistant coatings, thermal barrier coatings and other applications. The method produces an improved interface between the bulk substrate material and the adhered film because of the initial surface preparation techniques.
Cutting tools for cutting hard materials are subject to wear and failure directly related to the stresses created in cutting the hard material. To prolong the cutting tool life, such tools are fabricated from extremely hard materials, such as for example 1-15% Co/WC, Si.sub.3 N.sub.4, SiAlON, SiC or tool steel. Adherence of a thin film composed of an even harder and non-reactive material, such as for example diamond, TiN or BN, to the base material of the cutting tool can increase the strength and wearability of the cutting tool. To date, however, the techniques for adhering the film to the cutting tool substrate have not produced an optimum interface, and the film usually fractures or delaminates from the substrate after minimal use.
Improved thin film adhesion is also desirable in many other applications. These include situations where it is necessary to protect substrates from environmental, temperature or wear effects. For example, ceramic coatings such as TiN or MgO are useful for environmental and corrosion protection. Coatings such as yttria stabilized zirconia provide thermal barriers to nickel superalloys and the like.
It is an object of this invention to provide an improved substrate/film interface, whereby the adhesion of the film to the substrate, is greatly improved, such that delamination or failure will not occur during use.
It is a further object to provide such an improved interface by increasing the surface area of the base material prior to film deposition by using a laser technique to induce micro-scale surface structures, followed by chemical or physical vapor deposition of the film onto the substrate.